1. Field of the Invention
This invention relates to an electric motor provided with a breather used for ventilating the inside of the motor body of the electric motor in order to maintain pressure in the motor body at atmospheric pressure.
2. Description of the Prior Art
Heretofore, as a breather for introducing air in the motor body, there has been known a breather disclosed in Japanese Utility Model disclosure (kokai) No. 3-45056/91, for example.
Generally, the breather is formed in a pipe-like shape and so designed as to be fixed to a vent hole of an electric motor at one end of the tubular body, the other end of the tubular body of the breather is opened and directed downwardly.
In the electric motor provided with the breather of this kind, when an armature of the motor rotates according to power supply, coils of the armature generate heat by electric current flowing in the coils, whereby air in the motor body is heated and expanded. The expanded air is discharged through the breather. Thereafter, when the power supply is interrupted, the heated air in the motor body is cooled and contracts whereby the air is introduced on the inside of the motor body through the breather.
Furthermore, if the motor is splashed with water when the motor is supplied with an electric current and air in the motor body is heated at a high temperature, the motor is cooled by the water and the air in the motor body contracts. Also in this case, the outside air is introduced in the motor body through the breather.
However, if the electric motor having the breather is splashed with a large amount of water, especially on the breather, the opening of the tubular-shaped breather may be filled up with a waterdrop, and the waterdrop caught at the opening of the breather sometimes changes into membranous water and is held by the internal face of the tubular-shaped breather under the action of surface tension of water. Accordingly, there is a problem in the aforementioned conventional breather since there is the possibility that the water drop or the membranous water may be sucked and penetrate into the motor body if the air in the motor body contracts in the state where the water drop or the membranous water fills up the opening of the breather.
The breather described in the aforementioned document is provided with projections 4, 5 and 6 in a tubular body 2, and it is possible to prevent the water penetration in some degree, however it is difficult to form the plurality of the opposed projections alternatively in the tubular body of the breather.